1. Field of the Invention
The present invention relates to a vehicle drive incorporating a toroidal type continuously variable transmission and more particularly to such a drive for a full-time four wheel drive car in which a drive force is always transmitted to four wheels and for a front-engine front-wheel drive car.
2. Related Background Art
A toroidal type continuously variable transmission as shown in FIGS. 6 and 7 has been studied for use as an automobile transmission. As disclosed in Japanese Laid-Open Utility Model application Ser. No. 62-71465, in the toroidal type continuously variable transmission, an input disk 2 is supported coaxially to an input shaft 1 and an output disk 4 is fixed to an end of an output shaft 3. Trunnions 5 which are swung around respective pivot axes transverse to the input shaft 1 and the output shaft 3 are mounted on a support bracket arranged on an inner surface of a casing or in the casing in which the toroidal type continuously variable transmission is housed. Power rollers 7 are rotatably supported around displaceable shafts 6 arranged at the centers of the trunnions 5. The power rollers 7 are held between the input disk 2 and the output disk 4.
Arcuate input and output concave surfaces 2a and 4a are formed on the opposing surfaces at axial ends of the input disk 2 and the output disk 4. Peripheral surfaces 7a of the spherical convex power rollers 7 abut against the input concave surface 2a and the output concave surface 4a.
A loading cam type pressure device 8 is provided between the input shaft 1 and the input disk 2 to resiliently urge the input disk 2 to the output disk 4. The pressure device 8 comprises a cam plate 9 which rotates with the input shaft 1 and a plurality of (for example four) rollers 11 held by a holder 10. A cam surface 12 which comprises a circumferential uneven surface is formed on one surface (right surface in FIGS. 6 and 7) of the cam plate 9, and a similar cam surface 13 is formed on an outer surface (left surface in FIGS. 6 and 7) of the input disk 2. The rollers 11 are rotatable around an axis which is radial to the center of the input shaft 1.
When the cam plate 9 is rotated as the input shaft 1 is rotated, the rollers 11 are urged to the outer cam surface 13 of the input disk 2 by the cam surface 12. As a result, the input disk 2 is urged to the power rollers 7 and the input disk 2 is rotated by the engagement of the pair of cam surfaces 12 and 13 and the rollers 11. The rotation of the input disk 2 is transmitted to the output disk 4 through the power rollers 7 so that the output shaft 3 fixed to the output disk 4 is rotated.
When rotating speeds of the input shaft 1 and the output shaft 3 are to be changed, for example, when the deceleration is to be made between the input shaft 1 and the output shaft 3, the trunnions 5 are swung around the pivot shaft to the position shown in FIG. 6 to incline the displaceable shafts 6 so that the peripheral surfaces 7a of the power rollers 7 abut against a center portion of the input concave surface 2a and an outer portion of the output concave surface 4a, respectively. When the acceleration is to be made, the trunnions 5 are swung to the position shown in FIG. 7 to incline the displaceable shafts 6 so that the peripheral surfaces 7a of the power rollers 7 abut against the outer portion of the input concave surface 2a and the center portion of the output concave surface 4a. When the angles of inclination of the displaceable shafts 6 are selected to an intermediate state between those of FIGS. 6 and 7, an intermediate speed change ratio of the input shaft 1 and the output shaft 3 is attained.
Japanese Laid-Open Utility Model application Ser. No. 63-60751 and Japanese Laid-Open Patent application Ser. No. 2-163549 disclose the (tandem) arrangement of a pair of toroidal type continuously variable transmission as shown in FIGS. 6 and 7 in parallel relative to the direction of transmission of the power.
FIG. 8 shows a structure disclosed in the Japanese Laid-Open Utility Model application Ser. No. 63-60751. A rotating force applied to an input shaft 1 is transmitted to two output disks 4 from two input disks 2 supported around the input shaft 1 through power rollers 7. The output disks 4 are rotatably supported around the input shaft 1.
The rotating forces of the two output disks 4 are transmitted to a disk-like cam plate 14 through rollers 11. The rotating force transmitted to the cam plate 14 is transmitted to an output shaft 3 through gears 15 meshed with teeth formed on an outer periphery of the cam plate 14, transmission shafts 16 having ends thereof fixed to the gears 15, gears 17 fixed to the other ends of the transmission shafts 16 and a gear 18 meshed with the gears 17.
As shown in the simplified diagram of FIG. 9, in the toroidal type continuously variable transmission constructed as described above, the rotating force of the input shaft 1 which is driven by the engine 20 is transmitted to the two parallel toroidal type variable transmissions 21 and the outputs of the two toroidal type variable transmissions 21 are taken out by the output shaft 3.
Where such toroidal type continuously variable transmission is used as a transmission for a four-wheel drive apparatus, the driving force once concentrated to the single output shaft 3 is to be redistributed to the two front and rear drive shafts. The repetition of the concentration and the distribution of the rotating drive force causes complexity in construction and increases the power loss due to friction.
To avoid the above problem, it has been proposed, as shown in FIG. 9B, to separately take out the outputs of the two toroidal transmissions 21 by two output shafts 3a and 3b and drive the front wheels by the output shaft 3a and the rear wheels by the other output shaft 3b.
However, if the two toroidal type continuously variable transmissions as shown in FIGS. 6 and 7 are arranged in parallel, a number of bearings to rotatably support the elements are required and the construction becomes complex and the power loss increases.